This invention concerns apparatus for encoding video signal components to be combined, such as the luminance and chrominance components of an NTSC-type television signal, to facilitate the separation of such components without crosstalk artifacts.
It is well-known that the frequency interleaving of the baseband luminance and chrominance components of an NTSC-type television signal does not always permit the two components to be separated without crosstalk artifacts such as cross-color and cross-luminance artifacts. The cross-color artifact results from chrominance contamination of luminance information, and can be described as a scintillating rainbow pattern in parts of an image where diagonal high frequency luminance information is present, such as on a striped shirt. The cross-luminance artifact is sometimes referred to as the "hanging dot" artifact, and is visible in a system using a comb filter type luminance/chrominance separator. Cross-luminance results from luminance contamination of chrominance information particularly at vertical image transition regions.
Cross-color and cross-luminance artifacts are introduced at two places in the system. First, imperfect or incorrect chrominance/luminance separation at a television receiver causes luminance to be interpreted as chrominance and vice-versa. The second way in which cross-color and cross-luminance artifacts are introduced is in the encoding process itself, which frequency interleaves the luminance and chrominance components.
Various methods have been proposed to improve the separation of luminance and chrominance components at the receiver by reducing luminance/chrominance crosstalk artifacts. Some of these methods involve source and receiver processing schemes using line, frame and field comb filters, such as described by C. H. Strolle in "Cooperative Processing of Improved NTSC Chrominance/Luminance Separation", SMPTE Journal, August 1986. Another system for prefiltering luminance and chrominance information via multi-dimensional comb filters before being combined is disclosed by Faroudja et al. in "Improving NTSC to Achieve Near-RGB Performance", SMPTE Journal, August 1987.
The proposed methods which seek to eliminate luminance/chrominance crosstalk artifacts suffer from one or more practical drawbacks related to switching artifacts in motion adaptive processing systems, or to filtering complexity in terms of memory requirements and the number of filter taps, for example. The luminance/Chrominance separation system disclosed herein in accordance with the present invention uses a cooperative processing technique with matched encoding and decoding processes. The disclosed system exhibits perfect luminance/chrominance separation in the vertical and vertical-temporal directions with minimal image degradation, and avoids many of the drawbacks of the known systems. In addition, the disclosed system is compatible with the existing NTSC system.